Focused electron flow electron tubes for very high frequencies



June 14, 1960 w. VElTH ETAL 2,941,111

FOCUSED ELECTRON FLOW ELECTRbN TUBES FOR VERY HIGH FREQUENCIES FiledJuly 18, 1955 3 Sheets-Sheet 1 Fig. 1

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FOCUSED ELECTRON FLOW ELECTRON TUBES FOR VERY HIGH FREQUENCIES FiledJuly 18, 1955 3 Sheets-Sheet 3 Fig. La

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hired rates fiice aocusnn utncrnon snow: ELECTRON TUBES non VERY menFREQUENCIES Werner Veith and Paul Meyerer, Munich, Germany, assignors toSiemens & Halske Aktiengesellschaft, Munieh and Berlin, Germany, acorporation of Germany This invention is concerned with focused electronflow electron tubes for very high frequencies.

Focused electron flow is used in numerous tubes for very highfrequencies, particularly in tubes operating in the nature of travellingwave tubes, special means being in suchv cases required for guiding theelectron fiow along extended paths. Magnet coils traversed by currentare usually employed for thi Purpose. It is, however, in many casessuitable to use a magnet system containing permanent magnets.

Magnet systems having permanent magnets have been proposed for suchtubes, comprising a tubular interior wave guide provided at its endswith annular extensions connected at their outer margins with magnetrods. It is in numerous cases of tubes of this kind, for example,traveling wave tubes necessary, for the coupling of the high-frequencyenergy, to provide. the interior wave guide tube with a suitable hollowconductor; forming apertures corresponding to its cross-section. Thedistrubance of the rotation symmetry of the magnetic field, caused bysuch apertures may be held small if the tubular wave guide is steppedfollowing the apertured parts, that is, if such wave guide comprises arelatively wide portion fiom which extends a relatively narrow portionhaving a diameter which is considerably smaller than the length thereof.

It has now been discovered that the above noted construction bringsabout a deterioration of the field strength characteristics inlongitudinal direction of the magnet system, by causing an increase inthe field strength in the vicinity of the transition of the wave guidetube from the wide to the narrow portion thereof while causing decreasein the field strength at the other end of the magnet system. Thedecrease at the other end may be traced to the fact that the lines offorce are due to the potential drop prevailing at such other enddeflected in the direction of the axis. Auxiliary lines of forceresulting from the increased field strength enter after the transitionagain into the narrow guide tube because the condition, according towhich the tangential component of the excitation must be constant, isnot fulfilled for these lines of force.

The object of the invention is to correct the field characteristics ofthe magnetic field strength within the magnet system and to avoid aboveall a decrease of the field strength at the end thereof. In a variablefield tube, such decrease would cause splitting of the electron flow andtherewith an impermissible increase of the electron current flowing tothe delay line.

In order to effect such a correction of the field characteristics, theinvention proposes to provide for a narrow guide tube portion extendingfrom the relatively wide portion and exhibiting gradually decreasingmagnetically effective cross-sectional area. The decrease may be steadyor in small increments, from the point of transition from the wideportion to the other end of the narrow guide tube. In accordance withanother feature of the invent o th e ay e pro ed. mag ic. s unts for; he

g et y t m or. for other ae shbor nay em; c rt connected therewith, The.decrease, of; the magnetically effective cross-section may be; such thatthere, r It along the narrow inner space? dfi lfid' by the narrow guidetube asubstantially homogeneous distribution of the magnetic' fieldstrength.

The various; objects and. features of the invention will appear from thedescription which will be rendered below withreference to theaccompanying diagrammatic; drawings showing in simplified manner partsof a proposed atrangement and contrasted therewith embodiments ac,-cording to, the invention, with their parts. which are essent-ial forthe understanding thereof likewise, simplified and known parts omittedfor convenience. of represents: tion. In these drawings:

Fig. 1 shows the proposed arrangement;

Fig. 2 illustrates the axially directed field characteristic present inthe structure according to Fig. 1;

Fig. 3 indicates an embodiment according to the in vention;

Fig. 4a shows. a diagrammatic longitudinal section through a furtherembodiment; and

Fig. 4b is a transverse section taken along line 4b.?4b of Fig. 4a. t

The proposed arrangement of 'Fig. 1 is provided with a magnet systemincluding an inner flux guide tube comprising the relatively narrowportion 1 and the relatively wide portion 8 which is interconnected withthe narrow portion by means of a transverse wall 7. At the outer ends ofthe magnet system, there are provided annular end plates 2 and 3 and onthe outside is disposed a tubular permanent magnet or a numberof'rodeshaped permanent magnets as indicated at 4 and 5. A highfrequency input Wave guide enters the system at 6', requiring theenlargement of the inner space provided by the wide guide tube portion8. The magnetic lines of force are symbolically indicated by the arrows9.

Fig. 2 shows a curve indicating the field progressing in the structureaccording to Fig. 1 in axial direction. From the curve will be seen thefield strength increase in the vicinity of the transition from the wideto the narrow flux guide tube and the decrease thereof at the end of themagnet system which is due to the deflection of the lines of forcetoward the axis, caused by the potential drop obtaining at such end. Theauxiliary lines of force again enter the narrow flux guide tube afterthe transition point because the condition, according to which thetangential component of the excitation must be constant, is notfulfilled therefor.

If the magnetically effective cross-section of the flux guide tube orthe wall thickness thereof is now diminished or decreased, from thetransition point to the end of the narrow guide tube, continually or insmall steps or increments, there will result along such guide tube orportion a more or less steady increase of the excitation. The fieldprogression may be made homogeneous by suitable dimensioning of thedecrease of the magnetically effective cross-section of the narrow guidetube and consequent increase of excitation; moreover, if desired, thefield strength at the output of the tube may be increased. Means bywhich this may be done will now be explained with reference to Fig. 3showing an embodiment according to the invention.

In Fig. 3 are shown parts, simplified for convenience, of a travelingwave tube in which an electron stream coming from the cathode 11 afiectsa helical delay conductor 12 contained in a glass tube 10.

Following the cathode 11 are a Wehnelt cylinder 13 and furtherelectrodes 14 and 15 forming with the cath ode an electron radiationsource or system. At the end of the electron path is disposed a targetelectrode 16.

The parts of the magnetic system serving for the focused guiding of theelectron stream are indicated by like reference numerals as in Fig. 1.In the embodiment illustrated in Fig. 3, the narrow innerflux guide tube1 isformed interiorly flaring; in accordance with the 'desired fieldstrength increase, the flare of the-conical bore may be at an angle upto about 10. The inner flux guide tube thus has a wall thickness whichdiminishes gradually longitudinally thereof.

i In the embodiment shown in Figs. 4a and 4b, there is provided an innernarrow flux guide tube 17 which has not been altered as to the wallthickness thereof. A second tube 18 is, however, provided which isconnected magnetically in parallel with the tube 17 and exhibits thereduction of wall thickness throughout its length. As is clearlyapparent from Fig. 4b, this arrangement has the advantage that theinteriorly flaring tube 18 may be repeatedly'slotted, thus permittinglocalization,'at the rev sulting' air gaps, of the rotation unsymmetriesinwardly scattered by the positions of the magnet rods 19 to 26.

Changes may be made withinthe scope and spirit of theappended claims. aWe claim: a 1. A travelling wave tube device having a travelling wavetube including a vessel having a relatively wide por- I travelling wavetube closely adjacent thereto, the magnetically operatively effectivecross-sectional area of said narrow flux guide portion eflfectivelycontinuously decreasing throughout its length from adjacent saidtransverse wall toward the opposite end thereof to avoid respectivelyoccurrence of a field strength increase in the vicinity of the juncturethereof with said transverse wall and field strength diminution at theend thereof remote from said juncture.

2. A structure and cooperation of parts according to claim 1, comprisinga tubular member surrounding said narrow guidetube portion, and meansfor connecting said tion constructed to receive a portion of a highfrequency waveguide and a relatively narrow elongatedportion extendingtherefrom, and having for the guidance of the electron flow within theextended path of said vessel a magnet system including permanent magnetmeans extending'radially spaced from a tubular flux guide surroundingsaid vessel and forming with parts of said tubular flux guide at leastone closed unidirectional magnetic circuit, said tubular flux guidecomprising'a rela- ;tively wide portion terminating in a transverse walland 'a' relatively narrow elongated portion extending from saidtransverse wall for respectively embracing said wide and 'narrowportions of the vessel of said travelling wave tube,

said relatively wide portion of said tubular flux guide containing highfrequency input wave guide means, said relatively narrow elongated fluxguide portion surrounding the narrow elongated portion of the vessel ofsaid tubular member magnetically in parallel with such guide tubeportion.

3. A structure and cooperationof partsaccording to claim 1, comprising atubular member surrounding said narrow guide tube portion, and means forconnecting said tubular member magnetically in parallel with such guidetube portion, said tubular member having longitudinally extending slotsfo'rmedtherein.

4. A structure and cooperation of parts according to claim 1, comprisinga tubular member surroundingsaid narrow guide tube portion, and meansfor connecting said tubular member magnetically in parallel with suchguide tube portion, said tubular member having longitudinally extendingslots formed therein and producing along the inner space formed by saidnarrow guide tube portion a substantially homogeneous field strength.

References Cited in the tile of this patent UNITED STATES PATENTS

